Device for preventing the risk of fire due to burning or glowing particles in a pipeline

ABSTRACT

A preventive safety system may be used in a process in which loosely formed process material is produced in a first unit (1) and is transportable to a receiving, second unit (2), and in which process the treatment of material in the first unit is liable to generate a hazardous particle or particles which has/have a temperature which is sufficiently high to initiate burning and/or an explosion in at least the second unit. The requisite transportation of the loosely formed material between the first unit and the second unit is effected through the medium of a stabilizing zone (7), an indicating zone (8) operative in indicating the presence of hazardous high-temperature particles, and an extinguishing zone (9), wherein the indicating zone (8) includes one or more hazardous particle sensors, wherein the sensors coact with an indicating and activating unit (12) such that when the presence of hazardous high-temperature particles is detected by a sensor (10) a device (15) is activated by the indicating and activating unit. The device (15) is located in the extinguishing zone and functions to deliver an extinguishing agent and/or to remove said hazardous particles from the system. A detection-dependent intensity can be evaluated in the activating unit (12) and that measure or procedure which is most suitable at that time selected in the indicating and activating unit (12) from a number of available safety measures and safety procedures (19, 20, 21).

TECHNICAL FIELD

The present invention relates to a preventive safety system and thenparticularly, but not exclusively, to a system which can be applied in aprocess, normally an industrial process, in which loosely formedmaterial is produced in a first unit and transported from said unit to areceiving, second unit.

By loosely formed material, it is meant any type of material that can betransported by a vehicle gas or in a gas or gaseous mixture, normallyair, in which the particles of material are mutually discrete.

Material of the kind meant here may consist in extremely fine, dust-likeparticles. It may also consist in powdery material or granularparticles, and also wood chips, pellets, straw, and like transportablematerials.

The concept on which the present invention is based requires thetreatment of the material within the first unit to be liable to generateindividual particles or several discrete particles that have been heatedto a temperature which is sufficiently high to cause a fire and/or anexplosion within the selected transportation path and/or at least withinthe second unit.

The path along which the loosely formed material is transported betweenthe first unit and the second unit will typically include a stabilizingzone (or disturbance zone), an indicating zone which is operative inindicating the presence of hazardous high-temperature particles, aneffectuating zone, an extinguishing zone, and a risk zone.

The stabilizing zone is intended to enable those particles of low energycontent and which do not constitute a fire or an explosion risk withinthe downstream zones, and particularly the risk zone, to reduce theirenergy content so that these particles will not be indicated by theindicating zone located immediately downstream.

Located within the indicating zone are one or more sensors or detectorswhich are intended to indicate the presence of particles whose energycontents are sufficiently high to incite burning, i.e., fire, when theparticles arrive in the downstream zones and then particularly in therisk zone. The sensors are arranged to coact with an indicating andactivating unit such that when one of the sensors detects the presenceof such high-temperature particles, there is activated a device or anarrangement which delivers an extinguishing agent and/or removes saidparticles from the system and which coacts with the extinguishing zone.

The indicating zone is followed by an effectuating zone whose length isso adapted that, upon activation of a device within the extinguishingzone, the device will have time to form an extinguishing barrier beforeor when the particle or particles reach said zone.

The extinguishing zone may also have the form of a valve which functionsto deflect particle collections that include said high temperatureparticles from the transportation path leading to the risk zone.

DESCRIPTION OF THE PRIOR ART

A preventive safety system of the aforedescribed kind is known andmarketed by Firefly AB, Huddinge, Sweden. The purpose of the preventivesafety system is to indicate the presence of sparks and glowingparticles and to apply an extinguishing agent or a smothering agentwhich will prevent glowing particles from reaching a downstream processunit, such as a filter, a silo, or like device in which combustionand/or an explosion could otherwise occur.

Also pertinent to the present standpoint of techniques is the fact thatthe risk of fire and explosion in modern industrial processes increaseswith increasing and higher production rates and within larger productionplants.

As volumes of material that are transported have successively becomegreater, practical experience has shown that most fires and explosionsthat occur in modern process plants are caused by sparks, glowingparticles, and airborne burning flakes or the like. Although thesesparks, glowing particles, etc., have a very small energy content, theenergy content is, nevertheless; sufficiently high to initiate a fireand/or an explosion.

It is thus known to take certain measures or procedures in an attempt toindicate as quickly as possible those particles, and only thoseparticles, which in themselves give an incitement to fire and explosion,so as to be able to restrict the effects thereof.

One of the many fields of application to which the present inventionpertains is the case when paper pulp is milled to cellulose fluff whichis transferred to a silo through the medium of a pneumatic transportsystem.

In this regard, it has been necessary to include a stabilizing zone inthe transportation line of earlier known safety systems, whereby thesensor or detector is placed at such a distance from the producing unitthat any occurrent hazardous particles and/or sparks that may haveoccurred will have been rendered safe or extinguished.

It has also been found necessary to provide a sensor-includingindication zone and an effectuation zone wherein the distance betweenthe sensor and extinguishing equipment must be sufficiently long toenable an extinguishing zone to be effectuated prior to a detectedhazardous particle reaching a downstream risk zone.

It is also proposed that there is provided an extinguishing zone whoselength has been adapted so that any occurrent and detected hazardousparticles can be rendered harmless prior to reaching the risk zone.

Also proposed is the possibility of shutting down the air transportationmeans and of generating an inert atmosphere in the vicinity of the riskzone.

The second unit, i.e., the receiving unit, can also be defined as a riskzone, since this unit may consist in a volume in which the transportedproduct or material is so concentrated as to represent a serious fireand explosion risk.

SUMMARY OF THE INVENTION Technical Problems

When considering the state of the prior art as described above, it willbe seen that a technical problem resides in the significance of usingsensors which are so constructed as to enable a risk factor to beevaluated on the basis of the intensity of said individual or severalparticles heated to a temperature at which the initiation of a fireand/or an explosion can be expected in at least the second unit, and toevaluate on the basis of the risk factor thus obtained and with the aidof circuits included in the unit make a suitable selection of anappropriate measure or procedure to eliminate the fire incitement.

It will also be seen that in the case of a preventive safety system ofthe kind defined in the introduction, a technical problem resides in theability to provide conditions by means of which further conditions canbe created, with the aid of the indicating and activating unit, whichwill enable the individual or several hazardous particles or a fire tobe extinguished or eliminated effectively without needing to exceed toany great extent the effect of the requisite extinguishing measures orprocedures and/or the requisite duration of such measures or procedures,such as to cause harm to the material.

It will also be seen that a technical problem is one of providingconditions which will enable the evaluated and chosen measures orprocedures to be taken from a plurality of available devices and/or touse an existing device to a greater or lesser extent.

It will also be seen that a technical problem is one of creating withthe aid of the indicating and activating unit conditions such that theappropriate measures or procedures taken are dependent on the nature ofthe process itself, thereby enabling one and the same equipment to beused for different situations.

Another technical problem resides in realizing the conditions that arerequired in order to generate combined activation of a valve which willfunction to remove from the system material collections that includehazardous particles.

It will also be seen that a technical problem is one of creating withthe aid of said indicating and/or activating unit initiating processeswhich will activate the whole of a water-based extinguishing system oronly selected parts of said system, or which will fully or partiallyactivate the supply of a fire extinguishing or a glowing-particlesmothering gas, such as an inert gas or some other appropriate gas,depending on the seriousness of the hazard detected by the sensors.

Another technical problem resides in realizing those advantages that areafforded when the indicating and activating unit can be programmed,thereby enabling process-related conditions to be program-controlled.

It will also be seen that another technical problem is one of realizingthose advantages that are afforded when the indicating and activatingunit can be programmed while observing the construction and method ofoperation of the extinguishing equipment, such as to enable anextinguishing zone to be constructed immediately before and/or when ahazardous particle or particles reaches or reach the extinguishing zoneprior to entering the risk zone, and also to be able to observe theinstantaneous rate of particle transportation.

Solution

The present invention provides a solution to one or more of theaforesaid technical problems and takes as its starting point a knownpreventive safety system of the kind defined in the introduction.

According to the present invention, the detection-dependent intensity ofhazardous particles can be evaluated in the indicating and activatingunit, and the choice of an appropriate measure or procedure is effectedin said unit in accordance with conditions or provisions stored in saidindicating and activating unit.

According to proposed embodiments that lie within the scope of thepresent invention, the measure or procedure chosen by the unit is one ofa plurality of available devices and/or consists in the greater orlesser use of one and the same device.

According to the invention, the choice of a suitable procedure ormeasure can be made in accordance with the nature of the process andalso in accordance with other criteria which enable a preventive safetysystem to be used and also to be adapted to suit different processes.

One of the aforesaid measures or procedures may reside in the activationof a valve which functions to deflect a material collection whichincludes hazardous particles from the normal transportation path leadingto the risk zone.

According to another embodiment of the invention, the sensor or sensorswill be placed at a distance from said first unit such that producedparticles which have a low, risk-free energy content will be able topass respective sensors without initiating a safety process in saidunit.

The measure or procedure chosen may also consist in fully or partiallyactivating a water-based extinguishing system.

The measure or procedure may also consist in fully or partiallyactivating a gas, water vapor, or like fire-requiring extinguishingsystem.

It is also proposed that the unit can be programmed so as to be able toobserve process-related conditions.

According to another embodiment, the unit can be programmed so as totake into account the construction and method of operation of theextinguishing equipment fitted, so as to enable an effectiveextinguishing zone to be formed or constructed immediately before ahazardous particle enters the risk zone, in which regard informationrelating to the speed of transportation of the particles is required.

Advantages

Those advantages that are primarily afforded by an inventive preventivesafety system reside in the provision of conditions which will enableone single piece of equipment to be adapted to suit a number ofdifferent processes and, in response to the intensity of the detectionof several sensors, the indicating and activating unit is able to selectone of several available and suitable measures or procedures, such asactivating fully or partially a water-based extinguishing system, orfully or partially activating a gas, water vapor, or like system.

BRIEF DESCRIPTION OF THE DRAWING

An exemplifying embodiment of an inventive preventive safety systemwhich can be used within an exemplifying process will now be describedin more detail with reference to the accompanying drawing, in which

FIG. 1 is a block schematic illustrating generally a process in whichthere is used an indicating and activating unit according to the presentinvention;

FIG. 2 illustrates a device in the form of a water-bearing extinguishingsystem provided with several nozzles, this system being chosen fromamong several available devices;

FIG. 3 illustrates another of said available devices in the form of awater-carried extinguishing system which includes a system locking platethat can be released by explosion;

FIG. 4 illustrates a third embodiment of one of said available devices,in the form of a mist curtain and/or a gas release;

FIG. 5 is intended to illustrate how particles having different energylevels initiate different intensities in the sensor or sensors andtherewith create conditions for the selection of an appropriate measureor procedure; and

FIG. 6 illustrates one embodiment of a material deflecting valve.

DESCRIPTION OF EMBODIMENTS PRESENTLY PREFERRED

FIG. 1 illustrates a preventive safety system which can be used within aprocess, an industrial process, in which loosely formed process materialis produced within a first unit 1 and can be transported to a receiving,second unit 2, by means of a conveyor 3.

The invention is based on the assumption that material treated in theunit 1 will produce individual particles or several particles which areheated to a temperature at which the particle or particles is/are liableto initiate fire and/or explosion in the system. One example in thisregard is the disintegration of paper pulp which enters a mill 1 in thedirection of the arrow 4 and from which the ultimate cellulose fluff istransported to the second unit 2, in the form of a silo, on a conveyorpath 3 which includes a conduit system 7, 8, 9 with the aid of anairstream 6. Disintegration of the paper pulp in the unit 1 may resultin individual particles or several discrete particles being heated to atemperature which is sufficiently high to cause a fire and/or explosionat least within the second part or second unit 2, and also within theparticle transportation system 3.

Although the exemplifying embodiment is described with reference to thedisintegration of paper pulp which is transported to a silo with the aidof an air stream, it will be obvious that the inventive concept can alsobe applied in other fields and for other purposes.

Another requirement is that the particles resulting from saiddisintegration are transported as loose material by a gas or gasmixture, normally air.

Another requirement is that the nature of the treatment carried out inthe unit 1 is such as to be liable to produce particles whose heatcontent can constitute a risk of fire in the conduit system or in astorage space, i.e., in the so-called risk zone.

According to the present invention, the system 3 by means of which theloosely formed material exiting in the conduit 5 is transported betweenthe first unit 1 and the second unit 2 includes, among other things, astabilizing zone 7, an indicating zone 8 which functions to indicatehazardous high-temperature particles, and an extinguishing zone 9 whichprecedes the second unit or risk zone 2.

The indicating zone 8 includes initially a plurality of known sensors10, for instance of the kind described and illustrated in U.S. Pat. No.3,824,392 to Tibbling, or other types of sensors that are able to detectthe presence of such particles.

Several sensors 10 are able to coact with an indicating and activatingunit 12 via a line 11.

A high-temperature particle indicated by a sensor 10 will result in theunit 12 activating a device 15 which is associated with theextinguishing zone 9 and which delivers an extinguishing agent and/orremoves the hazardous high-temperature particles.

In accordance with the invention, the detection-dependent intensitysensed in one or more sensors 10 can be evaluated in a circuit 16included in the indicating and activating unit 12, and one of severalavailable, indicated, and suitable measures or procedures can beactivated in a calculating circuit 17 through the medium of a circuit18.

The measures activated in this way may include one of a number ofavailable devices, such as one of three devices 19, 20, and 21. Both themeasure activated and procedure activated depend on the nature of theactivation signal on the lines 19a, 20a or 21a.

Alternatively, one and the same device can be used to a greater or alesser extent, by modifying the signal on one of the lines.

The invention also provides the possibility of programming thecalculating circuit 17 so that the measure or procedure to be taken willbe chosen by the circuit in accordance with the nature of the process,which can be loaded through a circuit 25 coupled to the unit 12.

In this regard, the measure or procedure chosen may constituteactivation of the device 21 having a valve which is mounted in theconduit section 9 and which functions to deflect a particle collectionwhich includes said hazardous particles in accordance with FIG. 6, whichillustrates a valve flap 60 inclined at a position 60', shown in brokenlines, at which the flap functions to deflect particles into a dischargeconduit 61.

The discharge conduit 61 includes a further valve flap 62, which mayalso be moved to an open position. Also shown is a fire extinguishingsystem 63.

The sensor 10 is placed at a distance from the first unit 1 such thatgenerated particles of low energy contents will pass respective sensorswithout initiating activation of the unit 12 and therewith withoutinitiating a safety measure or procedure via the unit 18.

The aforementioned safety measures or safety procedures may also includethe activation of the whole of a water-based extinguishing system or ofsolely parts of said system, in accordance with FIG. 2, where differentnozzles of one of the exemplary safety measures 19 can be activated withthe aid of signals arriving on the lines 19a and 20a.

The signal on the line 20a will activate two solenoid valves 31 and 32,in response to which the material under transportation will be sprayedwith water held under pressure in the water delivery system 33.

The signal on the line 19a will activate one single additional solenoidvalve 34.

The water delivery system is shut down in response to a signal on theline 21a.

In this case, the calculating unit 17 will select a safety measure orprocedure and also the duration over which the safety measure orprocedure shall remain in effect, in a simple programmable manner.

The unit 12 may also be programmed via a circuit 26 for the purpose oftaking into account process internal conditions, such as the nature ofthe chosen material, a necessary time delay depending on the instantspeed at which material is transported, and where the instant speed canbe evaluated by a sensor 10a; and a signal corresponding to this speedis sent to the circuit 17 on a line 11a.

The unit 12 may also be programmed to take into account the constructionand method of operation of the extinguishing equipment, so that theextinguishing zone will become active immediately before a hazardousparticle or hazardous particles enters or enter said zone.

FIG. 3 illustrates a water-based extinguishing system which includes anexplosive locking plate release.

A solenoid valve is opened in response to a signal on the line 20a andthe locking plates 41, 42, and 43 are released in response to a signalon the line 19a, so as to activate the nozzles of the system. Theabsence of a signal on the line 20a causes the valve to close.

FIG. 4 illustrates an alternative embodiment of the invention for usewhen water cannot be used as an extinguishing agent in the extinguishingzone. In this case, extinguishing of the hazardous, high temperatureparticles is achieved by the device 20 which delivers CO₂, N₂, orsaturated steam or some similar agent.

A signal on the line 19a will activate steam injection equipment,whereas a signal on the line 20a will cause the valve of a gas bottle toopen, and a signal on the line 21a will cause the valve of a further gasbottle to open.

The valves remain open for the duration of the signal on respectivelines.

It is possible, in accordance with the invention, to chose one or moreof the aforesaid safety measures or procedures with the aid of thecircuit 18, in accordance with the level of sensed intensity and inaccordance with the chosen intensity levels.

FIG. 5 illustrates schematically the limit values for given signallevels delivered by the sensors 10, and also shows that the limit valuescan vary up and down depending on the nature of the process among otherthings.

Signal intensity beneath a given level 51 is ignored, such as the signal50.

The intensity of the signal 52 exceeds a level 53 and can be consideredto instigate the choice of limited extinguishment, for instance byactivating a nozzle 34 in FIG. 2, the delivery of steam in accordancewith FIG. 4, or some like measure.

The intensity of the signal 54 exceeds the level 55 and requires fulleffect and a well-balanced activation time.

The unit 12 may, of course, also coact with an alarm system in a knownmanner, via a line 32.

The sensor 10 may conveniently have the form of the sensor arrangementillustrated and described in a U.S. patent Ser. No. 06/624,486 entitled"Detector Arrangement" filed on Apr. 4, 1996.

It will be understood that the invention is not restricted to theaforedescribed and illustrated exemplifying embodiment thereof and thatmodifications can be made within the scope of the inventive concept asillustrated in the following claims.

I claim:
 1. A preventive safety system comprising:means for transportingmaterial between a first unit and a second unit, an indicating zone forindicating a presence of hazardous particles, an indicating andactivating unit, and an extinguishing zone having a device locatedtherein, the indicating zone including a hazardous particle sensor forcoacting with the indicating and activating unit, the device located inthe extinguishing zone including extinguishing means for delivering anextinguishing agent and removing means for removing said hazardousparticles from the system, the indicating and activating unitincluding:means for evaluating an intensity of hazardous particletemperature, means for selectively activating one of the extinguishingmeans and the removing means in response to the evaluating means, andmeans for selectively adjusting operation of the extinguishing means inresponse to the evaluating means.
 2. A system according to claim 1,wherein the extinguishing means is a plurality of spray nozzles.
 3. Asystem according to claim 1, wherein the removing means is a valve whichdeflects a particle collection containing said hazardous particles.
 4. Asystem according to claim 1, wherein the sensor is placed at a distancefrom the first unit such that generated particles of low energy contentwill pass the sensor without causing the means for selectivelyactivating to activate.
 5. A system according to claim 1, wherein themeans for selectively adjusting the operation of the extinguishing meanspartially activates a water-based extinguishing system.
 6. A systemaccording to claim 1, wherein the means for selectively adjusting theoperation of the extinguishing means partially activates theextinguishing means.
 7. A system according to claim 1, furthercomprising means for programming the indicating and activating unit. 8.A system according to claim 1, further comprising means for programmingthe indicating and activating unit such that the extinguishing meanswill be activated when at least one of the hazardous particles entersthe extinguishing zone.
 9. A system according to claim 1, wherein theextinguishing means is a system for delivering one of steam and gas. 10.A system according to claim 1, wherein the indicating zone includes aplurality of said sensors, all of said sensors for coacting with theindicating and activating unit.